Light sensitive polycarbonamide coatings for screen printing



United States Patent 3,245,792 LIGHT SENSITIVE POLYCARBONAMIDE COAT- INGS FOR SCREEN PRINTING Maximilian Karl Reichel and Wilhelm Neugebauer, Wiesbaden-Biebrich, Germany, assignors, by mesne assignments, to Azoplate Corporation, Murray Hill, NJ. No Drawing. Filed Sept. 26, 1960, Ser. No. 58,174 Claims priority, application Germany, Oct. 3, 1959, K 38,826 14 Claims. (Cl. 9635) The screen-printing industry today uses almost exclusively screen printing stencils prepared either directly or indirectly by photomechanical means. In the direct preparation of screen printing stencils, fabric is directly coated with a liquid colloid emulsion which is dried and then sensitized, if the light-sensitive substance, which when exposed to light has a tanning action on the colloid, has not already been dispersed throughout the emulsion. A photographic diapositive serving as a master is then placed, in a copying frame, upon the sensitized fabric and the material is exposed to light under the master. As a result of hardening, those portions of the colloid coating struck by light become insoluble in water and remain on the fabric during development, while those portions of the reproduction coating protected by the diapositive, and not struck by light, are washed out during development. The open parts of the fabric correspond to the original that is being copied and when printing is effected with the stencil, positive copies of the diapositive used are obtained.

In the indirect photomechanical preparation of screen printing stencils, the copy of the original is placed not on fabric provided with a reproduction coating and set up in a copying frame, but on a support with a light-sensitive colloid coating consisting, for example, of pigment paper or a transparent photographic film. After the exposed support has been placed on an intermediate base, e.g., consisting of glass or film, those portions of the light-sensitive coating protected from the light under the diapositive are washed away with water and then the hardened colloid image is transferred to the screen fabric.

Screen printing stencils prepared by the direct process are characterized by accuracy of registration and great resistance, but fine text and drawing lines always have a serrated edge, even if the finest fabrics are used, because the light-sensitive coating is embedded in the fabric between the strands. With the indirect process there is the great advantage that the marginal sharpness of the tanned image surfaces is not dependent on the mesh apertures of the fabric. in this case, the tanned image is on the tissue of the stencil so that it is also possible for the mesh apertures to be partially covered. Microscopically sharp printing plates are obtained therewith, such as are necessary for the finest text, line and screen work. The greater complication involved in the indirect process and the fact that owing to the wet developing process the original is not always reproduced exactly true to size are factors which have hitherto been accepted as unavoidable.

The present invention relates to reproduction material, the use of which in the preparation of screen-printing stencils results in great advantages and makes possible a considerable simplification in the indirect method for the preparation of screen-printing stencils, as discussed above. Insofar as the actual preparation of the screens is concerned, the new process is itself a part of the invention. The reproduction material of the invention is characterized in that it consists of a support (e.g. paper, plastic foil, metal foil), a water-soluble colloid layer directly adherent to the support, and a synthetic ice polyamide coating applied to this colloid layer containing as light sensitive substances aromatic azido compounds.

The synthetic polyamides to be used for the preparation of the reproduction coatings of the invention are obtained in a manner known per so, by polycondensation. They may, for example, be formed by polycondensation of a w-aminocarboxylic acid or the lactam thereof, by polycondens-ation of a mixture of a w,w-dicarboxylic acid with an equivalent quantity of a w,w'-diamine, or by polycondensation of mixtures of equivalent quantities of a number of w,w'-dicarboxylic acids with w,w-diamines. In the synthetic polyamides suitable for the reproduction coatings of the invention and formed by polycondensation of a w-aminocarboxylic acid or two reaction components, some of the hydrogen atoms on the amide nitrogen in the carboxylic acid amide groups contained in the macromolecules thereof must be substituted by alkyl, oxyalkyl, or, preferably, alkoxyalkyl. Synthetic polyamides of this type are suitable for the purposes of the invention even if they have been subjected before the partial N-alkoxyalkylation process to a partial depolymerization.

For the preparation of the reproduction coatings, synthetic polyamides formed by the mutual polycondensation of more than two monomeric reaction components are also suitable, e.g., those formed from at least one w,w' dicarboxylic acid, at least one w,w'-diam-ine, in equivalent quantities, and at least one w-amino carboxylic acid, in each case the proportion of w-aminocarboxylic acid in the polycondensate being 10 to 40 percent by weight, preferably 20 to 40 percent. F or coating purposes, these polyamides are used in 2-10 percent, preferably 3-6 percent alcoholic solutions. The employment of polyamides of this type for the preparation of light sensitive coatings from which tanned images for use in association with screen printing stencils is described in German Patent 954,308. I

A process for partial alkylation, oxyalkylation and alkoxyalkylation is described in US. Patent No. 2,430,860. For example, the alkoxyalkylation may consist of dissolving, on a steam bath, 100 g. of poly-e-caprolactam, with a K-value of 63-69, in 300 ml. of glacial acetic acid and ml. of percent formic acid, and the slow :dropwise introduction into this mixture of a hotfiltered solution of g. of paraform-aldehyde in 250 ml. of methanol at 70 C. with stirring, a small quantity of solid sodium hydroxide being added for the depolymerization of the paraformaldehyde. After the reaction mixture has been stirred for four IhOHIS at 70 C., it is cooled to 5560 C. and then introduced dropwise, with vigorous stirring, into an excess 5 percent ammonia solution. The partially N-methoxymethylated poly-e-caprolactam immediately precipitates out in flakes. It is washed a number of times with cold water, decanted, separated by suction filtration, washed free of ammonia and dried in the air. The yield, in relation to the starting product, is nearly quantitative. Instead of methyl alcohol, ethyl alcohol, allyl alcohol or n-propyl alcohol can be used for the N-alkoxyalkylation with the same results.

These N-alkoxylalkylated polyamides are characterized in that 1040 percent, preferably 20-40 percent, of the carboxylic acid amide groups contained in the macromolecules are substituted at the amide nitrogen, while the intrinsic viscosity value (1 at 0.51.0, preferably 0.65- 0.85 and the K value at 63 -69 (after Fikentscher, cf. W. Schaefer, Einfuhrung in das Kunststoifgebiet (1951), p. 104) are relatively unchanged in comparison to the starting material.

Partially depolymerized synthetic polyamide, e.g., from poly-e-caprolactam, is obtained as follows: 30 g. of polye-caprolactam with a K-value of 63-69 and an intrinsic viscosity of 0.65-0.85 are dissolved over a period of one hour on a steam bath under reflux in a mixture consisting of 150 ml. of 90 percent formic acid, 50 ml. of concentrated hydrochloric acid) or 20 ml. of concentrated sulphuric acid) and 100 ml. of methyl alcohol. The reaction mixture is then cooled to 5060 C. and introduced dropwise, with vigorous stirring, into an excess of a percent ammonia solution. The polyamide separates out immediately in the form of white flakes. Stirring is continued for one hour at room temperature and the polyamide is then washed a number of times with cold water, decanted, separated by suction filtration, washed free of ammonia and dried in the air. The yield of partially depolymerized polycaprolactam, based upon the starting material, is nearly quantitative. The partially depolymerized poly-e-caprolactam has a K-value of 30-35 and an intrinsic viscosity (1;) of 0.15- 0.21.

The same process being followed, other substances, e.g., poly-e-capryllactam, polycondensed adipic acid hexamethylene diamine or polycondensed sebacic acid hexamethylene diamine may be used instead of the poly-ecaprolactam. Partially depolymerized polymides, characterized by a K-value of 58-60, as compared with that of 7172 for the starting material, are obtained.

The aromatic azido compounds to be used as light sensitive substances in the reproduction coatings are, constitutionally, p-azido-styryl benzenes or p-azidostyryl ketones and correspond to the general formula In the formula, R is an aliphatic or aromatic or heterocyclic radical, of which the following are exemplary:

III II OH O X is hydrogen or a group forming a water-soluble alkali metal salt or the group SO -HNaryl, in which aryl may be substituted, and Y is hydrogen, an alkyl group or a carboxyl group.

The following are exemplary of the light-sensitive aromatic azido compounds which under the influence of light exert a tanning action on the polyarnides:

FORMULA 1 H H N3 C=CCH3 I SO Na FORMULA 2 FORMULA '3 S O 3N3 S OKNa FORMULA 4 C O ONa C O 0N2.

FORMULA 5 FORMULA 8 FORMULA 11 S 031% S OsNa.

FORMULA 12 FORMULA 13 H CH3 FORMULA 14 FORMULA 16 FORMULA 17 FORMULA 18 FORMULA 19 r t t t N C=CCC=CH2 SOaNa FORMULA 20 C1 G1 I l -G OsNa OaNa FORMULA 21 4-azido-w-methylstyryl-2-sulfonic acid sodium salt, corresponding to Formula 1, is prepared by the method described in the Journal fiir praktische Chemie, vol. 152 (1939), pages 237266. After crotonic acid has been condensed With diazotized 4-nitroaniline-2-sulfonic acid in the presence of cupric chloride and acetone, the nitro compound is reduced catalytically to the 4-aminostyryl compound, which is then diazotized and reacted With sodium azide.

4-azido-stilbene-2-su1tonic acid sodium salt, corresponding to Formula 2, is prepared by the process described in Journal fiir praktische Chemie, vol. 152 (1939), pages 237-266. Instead of crotonic acid, cinnamic acid is used.

4,4-diazidostilbene-2,2-disulfonic acid sodium salt, corresponding to Formula 3.

4,4'-diazidostilbene-2,2'-dicarboxylic acid sodium salt, corresponding to Formula 4.

4,4-diazidostilbene-a-carboxylic acid sodium salt, corresponding to Formula 5.

4-aZido-benzalacetone-2-sulfonic acid potassium salt, corresponding to Formula 6.

Disodium salt of 4-azidobenzal-pyroracemic acid-2- sulfonic acid, corresponding to Formula 7.

4,4-diazidostilbene corresponding to Formula 8, prepared by catalytic reduction of 4,4'-dinitrostilbene to 4,4-diaminostilbene, which is then tetrazotized and converted into the diazidostilbene by reaction with sodium azide.

4-azidobenzal-acetophenone-2-sulfonic acid sodium salt, corresponding to Formula 9.

4 azido 2 hydroxy dibenzalacetone 2 sulfonic acid sodium salt, corresponding to Formula 10.

4-aZido-4-fluorostilbene 2,2 disulfonic acid sodium salt, corresponding to Formula 11, is prepared by the thermal decomposition of the diazonium borofluoride of 4-nitro-4'-aminostilbene 2,2 disulfonic acid, reduction, diazotization and reaction With sodium azide.

4,4'-diaZido-bis-(styryl-ketone)-2-sulfonic acid sodium salt, corresponding to Formula 12 is prepared by the condensation of 4-azido-benzaldehyde 2 sulfonic acid sodium salt with 4-azido-benzalacetone by a process analogous to that described in German Patent No. 752,852.

4-(4'-azido-fl-methylstyryl)-pyridine, corresponding to Formula 13, is prepared by the condensation of 4-nitrobenzaldehyde with ethyl pyridine by the process described in the Journal of the American Chemical Society, vol. 76 (1952), pages 39863987, i.e., catalytic reduction of the nitro compound to the corresponding amino compound, diazotization of the latter and conversion of the diazo compound by means of sodium azide.

4-azidostilbene-2,2-disulfonic acid sodium salt, corresponding to Formula 14, is prepared from 4-nitro-4- aminostilbene-2,2-disulfonic acid. This is diazotized and the diazo compound is boiled in absolute alcohol, the nitro compound is catalytically reduced, the amino group is diazotized and final conversion is by means of sodium azide.

2- (4-azidostyryl) -6-azido-benzimidazole, corresponding to Formula 15, is prepared by the condensation of 4- nitrobenzaldehyde with 2-methyl-S-nitrobenzimidazole, catalytic reduction of the dinitro compound, diazotization of the diamino compound and conversation of the tetrazo compound with sodium azide.

5- (4-azidophenyl)-2-(4"-azidostyryl) furan, corresponding to Formula 16, is prepared by a process analogous to that described in connection with the compound of Formula 1. Furyl acrylic acid instead of crotonic acid is condensed with two moles of diazotized p-nitraniline, the dinitro compound is catalytically reduced, and the tetrazo compound is reacted with sodium azide. 4,4'-diazidostilbene-2,2-disulfonamide, corresponding to Formula 17, is prepared from 4,4'-dinitrostilbene-2,2'- disulfonyl chloride by reaction with ammonia, reduction of the dinitro compound, tetrazotization and conversion to the diazide by means of sodium azide.

4,4-diazidostilb'ene-2,2-bis-sulfianilide, corresponding to Formula 18, is prepared by condensation of 4,4-dinitrostilbene-2,2'-disulfonyl chloride With aniline, catalytic reduction of the dinitro compound and conversion of the tetrazo derivative by means of sodium azide.

4-azido-benzal-methyl-vinyl-ketone-2-sulfonic acid sodium salt, corresponding to Formula 19, is prepared by condensation of 4-azido-benzaldehyde-2-sulfonic acid sodium salt With methyl vinyl ketone, by a process analogous to that described in German Patent No. 752,852.

4,4-diazido-S,5-dichlorostilbene-2,2'-disulfonic acid sodium salt, and corresponding to Formula 20, is prepared from 4,4-dinitro-5,5'-dichlorostilbene-2,2'-disulfonic acid sodium salt by catalytic reduction, tetrazotization and con version with sodium azide.

4,4'-diazidostilbene-2,2-bis (sulfanilide-4" hydroxyethyl-ether) corresponding to Formula 21, is prepared by condensation of 1 mole of 4,4'-diazidostilbene-2,2-disulfonyl-chloride with 2 moles of ,B-hydroxy-p-phenetidine.

Suitable supports for the synthetic polyamide reproduction coatings include paper with a smooth surface or plastic foils, e.g., foils of superficially hydrolized celamide used for the formation of the reproduction coating from penetrating into the support.

The preparation of the reproduction material is as follows: The support is coated with a 2-5 percent, preferably 3-4 percent, aqueous solution of a water-soluble colloid. After the water-soluble colloid coating has dried on the support, the light-sensitive alcoholic solution of synthetic polyamide is applied to the colloid coating; 2-8 percent, preferably 3-6 percent, alcoholic solutions of synthetic polyamide are used or, in some cases, a mixture of a number of synthetic polyamides of the above type. The solvents for the polyamides used for the preparation of the reproduction coatings are 75-96 percent, preferably 80-85 percent, lower aliphatic alcohols, e.g., methyl alcohol, ethyl alcohol, and isopropyl alcohol. The proportions of polyamide to aromatic azido compound in the coating solutions are 2-4 parts of dry polyamide to one part of azido compound. In order that the tanned image will become visible and the quality thereof can be readily examined, if desired dyestuffs may be added to the coating solutions in quantities of from 0.1 to 0.5 percent by weight. The dyestuffs used are those which have low U.V. absorption, e.g., Methyl Violet BB (Schultz Farbstofftabellen, 7th edition, vol. I (1931), page 327, No. 783), Patent Blue V (ibid., p. 349, No. 826), Rosaniline Hydrochloride (ibid., p. 324, No. 780), and New Fuchsine (ibid., p. 326, No. 782).

The reproduction material has, for practical purposes, unlimited shelf-life. When the reproduction coating is exposed under a transparent master (diapositive) to light,

the time-consuming process involving the application of bichromate solution is, in this case, superfluous and those portions of the polyamide coating tanned by the action of light are so resistant that the coating can be directly transferred to the screen surface.

The present invention includes, as mentioned, above, the preparation of screen printing stencils by means of the reproduction material of the invention. This process of preparation, which can be counted among the indirect processes, is very simple in comparison with those hitherto known. The reproduction material of the invention is placed behind a diapositive, coating to coating, and exposed preferably in a printing frame to a light source emitting actinic light, e.g., an l8-amp carbon arc lamp at a distance of about cm., for one to two minutes. The exposed reproduction material is transferred dry to the outer side of the screen tissue stretched on a frame. The screen tissue may, for example, be a nylon tissue, a tissue of the type commercially available under the trademark Perlon or a tissue consisting of a linear polyester or a metal gauze wetted with 60-80 percent alcohol. For the purposes of transfer, the exposed reproduction material is held down with weights or it is pressed firmly on the tissues by means of a hard rubber roller. Screen tissue and exposed reproduction material are then left in position for 3-5 minutes at room temperature, after which water treatment is performed. For example, the paper side of the reproduction material, while pressed upon the screen-printing frame is held under running water and, after about 2-3 minutes, the softened support is peeled off the reproduction material. The parts of the reproduction coating that have been hardened by light adhere firmly to the screen tissue. The stencil is dried in hot air and at this stage any portions of the printing surface of the stencil that have not been completely bared can readily be made ink-conductive by means of methyl alcohol or ethyl alcohol or isopropyl alcohol applied by means of a spray gun or dabbed on with cotton. It may be advantageous for the inside of the framed printing screen, i.e., the back of the stencil, to be sprayed or dabbed in this way and then dried in hot air.

Thus, in an extremely simple manner screen printing stencils are obtained with tanned coatings which adhere exceptionally Well to the screen tissue without pretreatment and are suitable,-without strengthening, for largescale runs, in particular for mechanical screen printing and film printing. The insolubility of the hardened polyamide coating in hot water, even in boiling water, and the excellent resistance thereof to ink containing a high percentage of caustic alkali enable it to be used in conjunction with the naphthol AS inking method for screen printing and film printing. The insolubility of the hardened polyamide coating in the usual solvents such as acetone, cyclohexanone, ether, ethyl acetate, butyl acetate, glycol, alcohol, benzene and its homologues and chlorinated hydrocarbons, enable dyestuffs and inking processes to be used, which are not capable of being used with screen printing stencils, with light-hardened coatings of water soluble colloids such as gelatine, polyvinyl alcohol and similar substances. Thus, new fields in mechanical screen printing and film printing are opened up. As the screen-printing and film stencils are not affected by oils and glycerine, practically any method of coloring can be used therewith.

The particular advantages of the reproduction material consist in its, practically speaking, unlimited shelf life in the unexposed state which has already been emphasized above and which has not been even approached by any of the reproduction materials hitherto known that are suitable for the preparation of screen printing stencils; in the possibility, offered by the good shelf life, of a stock of exposed material being accumulated, thus enabling the production of stencils to be performed quickly, unrestricted by time limitations, so that rational working systems can be utilized. These favorable results were not in any way to be foretold, as in view of thegreat solubility of the synthetic polyamides in aqueous alcohols at room temperature and of the inadequacy for practical purposes of the tanning action hitherto obtained with coatings of water soluble colloids made light-sensitive with aromatic azido compounds, suitability of the synthetic polyamides for the preparation of light-sensitive materials for screen and film printing was not to be expected. It is particularly surprising that the brief wetting of the screen tissue with aqueous alcohol, e.g., 60 percent, is adequate to effect dry transfer directly to the screen tissue of the still undeveloped tanned image.

The invention will be further illustrated by reference to the following specific examples:

Example 1 Paper with smooth surface or a transparent foil, of 8-12 thickness, of superficially hydrolyzed cellulose acetate is coated at room temperature with a 3 percent gelatine solution and the coated material is dried at 80 C. The alcoholic solution described below, containing synthetic polyamide and aromatic azido compound, is then applied to the dry gelatine coating and dried at 90-95 C. Reproduction material characterized by almost unlimited shelf-life and of exceptional suitability for the production of screen printing stencils is obtained.

The light-sensitive solution is'prepared as follows:

200 ml. of a 10 percent solution, prepared with percent ethyl alcohol, of a polyamide formed from adipic acid hexamethylene diamine and e-caprolactam in proportions by weight of 3:2 are thoroughly mixed at 45-50 C., with continuous stirring, with a solution obtained by the brief heating on the steam bath of 10 g. of 4,4-diazidostilbene-2,2'-disulfonic acid sodium salt in a mixture of 12.5 ml. of water and 37.5 ml. of glycol monornethylether. The mixture is made up to 500 ml. with 96 percent ethyl alcohol.

Example 2 Paper with smooth surface or a transparent film made, for example, of stretched and heat-fixed polyterephthalic acid glycol ester is coated at room temperature with a 4 percent solution of Le Pages photographic size and dried at 75-80 C. The light-sensitive alcoholic solution described below, containing synthetic polyarnide and aromatic azido compound, is applied to the dry size coating and dried at 90-95 C. A light-sensitive material is obtained which is highly suitable for screen and film printing and in the unexposed state has almost unlimited shelf-life and can be used with great advantage for the preparation of screen printing stencils.

The light-sensitive solution is prepared as follows:

200 ml. of a percent solution, prepared with 80 percent ethyl alcohol, of a polyamide formed from adipic acid hexamethylene diamine, adipic acid 4,4'-diarninodicyclohexyl methane and e-caprolactam in the proportions by weight of 1:1:1 are thoroughly mixed at 45-50 C., with stirring, with a solution prepared by the brief heating on a steam bath of 10 g. of 4,4diazidostilbene-2,2'- disulfonic acid sodium salt in a mixture of 12.5 ml. of water and 37.5 ml. of glycol monomethyl ether. The mixture is made up to 500 ml. with 96 percent ethyl alcohol.

Example 3 Paper with smooth surface or a transparent polyvinyl chloride film is coated first with a 3 percent polyvinyl alcohol solution at room temperature and the coated material is dried at 7580 C. The light-sensitive alcoholic solution described below, containing synthetic polyamide and aromatic azido compound, is applied to the dry polyvinyl alcohol coating and is dried at 90-95 C. Lightsensitive material is obtained which has almost unlimited shelf-life in the unexposed state and is highly suitable for the preparation of screen printing stencils.

The light-sensitive solution is prepared as follows:

200 ml. of a 10 percent solution, prepared with 80 percent ethyl alcohol, of the polyamide N-methoxy-rnethyl-poly-e-caprolactam, with a K value of 63.2, corresponding to an intrinsic viscosity (77) of 0.65, and a methoxy content of 7.5-8 percent, corresponding to 38-40 percent of substituted carboxylic acid amide group, are thoroughly mixed, with continuous stirring at 45-50 C., with a solution of 6 g. of 4,4-diazidostilbene in 50 m1. of glycol monomethylether. The mixture is made up to 300 ml. with 96 percent ethyl alcohol. Instead of the N-methoxymethyl-poly-e-caprolactam, the same quantity of N-ethoxypoly-e-caprolactam or N-propenoxy-poly-e-caprolactam or N-propoxy-methyl-poly-e-caprolactam can be used with equally good results.

Example 4 Paper with smooth surface or a transparent biaxially stretched and heat-fixed polyterephthalic acid glycol ester film is coated with a 4 percent solution of Le Pages photographic size at room temperature and the coated material is dried at 75-80 C. The light-sensitive alcoholic solution of synthetic polyamide and aromatic azido compound described below is applied to the dried size coating and dried at 9095 C. The reproduction material keeps for an almost unlimited period without alteration in the light-sensitivity thereof. It is suitable for the preparation of screen printing stencils.

The light-sensitive solution is prepared as follows:

200 ml. of a 10 percent solution, prepared with 80 percent ethyl alcohol, of a polyamide consisting of partially depolymerized and partially N-methoxy-methylated polycondensate of adipic acid hexamethylene diamine with a K value of 57.8, corresponding to an intrinsic viscosity (1;) of 0.58 (methoxy content: 8 percent), are

10 thoroughly mixed, at 45-50 C., with stirring, with a solution of 6 g. of 2-(4'-azidostyryl)-6-azido-benzimidazole corresponding to Formula 15:

in 50 ml. of glycol monomethylether, The mixture is made up to 500 ml. with 96 percent ethyl alcohol. Instead of 6 g. of 2-(4'-azido-styryl)-6-azido-benzimidazole, 10 g. of 4-(4-azido-B- .ethylstyryl)-pyridine (Formula 13) or 6 g. of 4,4-diazidostilbene-2,2'-disulfonamide (Formula 17) or 6 g. of 4,4'-diazidostilbene-2,2'-bissulfanilide (Formula 18) can be used.

Example 5 Paper with smooth surface or a transparent, biaxially stretched and heat-fixed polyterephthalic acid glycol ester film is coated with a 4 percent solution of Le Pages photographic size at room temperature and the coated material is dried at 7580 C. The light-sensitive alcoholic solution of synthetic polyamide and aromatic azido compound described below is applied to the dried size coating and it is dried at 90-95 C. The shelf-life of this reproduction material in the unexposed state is outstanding. It is used with advantage, for the preparation of screen printing stencils.

The light-sensitive solution is prepared as follows:

200 ml. of a 10 percent solution, prepared with percent ethyl alcohol, of a mixture consisting of equal parts by weight of N-methoxy-methylated polycondensate of adipic acid hexamethylene diamine and polyamide obtained by mutual polycondensation from adipic acid hexamethylene diamine, adipic acid 4,4-diamino-dicyclohexyl methane and e-caprolactam in the proportions by weight of 1:1:1 are thoroughly mixed, with stirring, at 4550 C., with a solution, prepared by heating on a steam bath, of 6 g. of 4,4'-diazidostilbene-2,2'-dicarboxylic acid sodi um salt (Formula 4) or 6 g. of 4,4-diazido-stilbene-acarboxylic acid sodium salt (Formula 5) or 10 g. of 4- azidobenzalacetone-Z-sulfonic acid sodium salt (Formula 6) or 10 g. of 4-aziclo-4-fluoro-stilbene-2,2-disulfonic acid sodium salt (Formula 11) or 6 g. of 4,4-diazido-5,5'-dichloro-stilbene-2,2-disulfonic acid sodium salt (Formula 20) in a mixture of 12.5 ml. of water and 37.5 ml. of ethyleneglycol monomethylether. The mixture is made up to 500 ml. with 96 percent ethyl alcohol.

Example 6 Paper having a smooth surface is coated with a 4 percent aqueous solution of polyvinyl alcohol at room temperature and dried at 7580 C. The light-sensitive alcoholic solution of synthetic polyamide and aromatic azido compound described below is applied to the polyvinyl alcohol layer and it is again dried at -95 C. The lightsensitive material thus obtained is exposed under a diapositive and then placed coated side on a tissue stretched in a frame and backed by a rubber mat. Immediately preceding this procedure, the tissue has been wetted with a 65 to 75 percent (by volume) aqueous alcoholic solution containing, per 1000 parts by volume of solution, 30 parts by Weight of N-methoxy-methyl-poly-e-caprolactam, 0.5 percent of formaldehyde, and 0.01 part by volume of concentrated hydrochloric acid. On the uncoated side of the exposed material, there are placed first a wetted felt web and then a wood or metal plate, which is subsequently loaded with weights. After 3 to 5 minutes, the Weights, the metal plate, and the felt web are removed and the paper support is cautiously peeled off. The screen printing stencil thus obtained is treated with cold running water and dried at 90 to 100 C. It may be used for printing the most different kinds of materials, such as paper, metals, ceramic, plastics, and fabrics (so-called film printing).

The light sensitive solution is prepared as follows: 200 ml. of a percent solution, prepared with 80 percent ethyl alcohol, of N-methoxy-methylpoly-s-caprolactam having a K-value of 63.2 corresponding to an intrinsic viscosity of 0.65, and a methoxy content of 7.5 to 8 percent corresponding to 38-40 percent of substituted carboxylic acid amide groups, are mixed at 45- 50 C., with thorough stirring, with a solution of 10 g. of 4,4-diazido-stilbene-2, 2'-disulfonic acid sodium salt in a mixture of 12.5 ml. of water and 37.5 ml. of ethylene-. glycol monomethyl ether. The mixture thus obtained is made up to 500 ml. with 96 percent ethyl alcohol.

It Will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is:

1. A process for making screen printing stencils which comprises exposing a coated support material to light under a master, the coating comprising a first layer of a water-soluble colloid and a second layer comprising an ethyl alcohol-soluble synthetic linear polycarbonamide and an aromatic azido compound having a vinyl group in the para position, pressing the exposed coating on a screen wetted with a solvent, whereby the coating is transferred to the screen, washing the coating with water to remove the non-hardened portions thereof, and drying the screen and coating not removed by the Water wash.

2. A process according to claim l in which the solvent is an aqueous alcohol.

3. A process according to claim 1 in which the polycarbonamide is formed by polycondensatio-n of a compound selected from the group consisting of a w-aminocarboxylic acid and the lactam thereof, and in which polycarbonamide about 10 to 40% of the hydrogen atoms on the amide nitrogen in the carboxylic acid amide groups are replaced by a radical selected from the group consisting of alkyl, oxyalkyl and alkoxyalkyl.

4. A process according to claim 1 in which the polycarbonamide is formed by polycondensation of a w,w'- dicarboxylic acid with a w,w-diamine, and in which polycarbonainide about 10 to 40% of the hydrogen atoms on the amide nitrogen in the carboxylic acid amide groups are replaced by a radical selected from the group consisting of alkyl, oxyalkyl and alkoxyalkyl.

5. A process according to claim 1 in which the polyamide is formed by polycondensation of a w,w-dicarboxylic acid, a w,w'-diamine and a w-aminocarboxylic acid.

6. A process according to claim 1 in which the azido compound is a p-azidostyryl benzene.

7. A process according to claim 1 in which the azido compound is a p-azidostyryl ketone.

8. A process according to claim -1 in which the azido compound has the formula in which R is an aryl group, and Y is selected from the phatic, aromatic, and heterocyclic radicals, X is selected from the group consisting of hydrogen, a water-soluble alkali metal salt-forming group and the group in which R is an aryl group, and Y is selected from the group consisting of hydrogen, an alkyl group and a carboxyl group.

9. A process for making screen-printing stencils which comprises exposing a coated support material to light under a master, the coating comprising a first layer of gelatin and a second layer comprising 4,4'-diazidostilbene-2,2'-disulfonic acid sodium salt and a linear polyoarbonamide formed from a salt of adipic acid and hexamethylene diamine and e-caprolactam, pressing the exposed coating on a screen wetted with an aqueous alcohol, whereby the coating is transferred to the screen, washing the coating with water to remove the non-hardened portions thereof, and drying the screen and coating not removed by the water wash.

10. A process for making screen printing stencils which comprises exposing a coated support material to light under a master, the coating comprising a first layer of photographic size and a second layer comprising 4,4- diazidostilbene-2,2-disulfonic acid sodium salt, and a linear polycarbonamide formed from a salt of adipic acid and hexamethylene diamine, adipic acid 4,4-diaminodicyclohcxyl methane and e-caprolactam, pressing the exposed coating on a screen wetted with an aqueous alcohol, whereby the coating is transferred to the screen, washing the coating with water to remove the non-hardened portions thereof, and drying the screen and coating not removed by the water wash.

11. A process for making screen printing stencils which comprises exposing a coated support material to light under a master, the coating comprising a first layer of polyvinyl alcohol and a second layer comprising 4,4- diazidostilbene and N-methoxy-methyl-poly-e-caprolactam, pressing the exposed coating on a screen wetted with an aqueous alcohol, whereby the coating is transferred to the screen, washing the coating with water to remove the non-hardened portions thereof, and drying the screen and coating not removed by the water wash.

12. .A process for making screen-printing stencils which comprises exposing a coated support material to light under a master, the coating comprising a first layer of photographic size and a second layer comprising 2-(4' azidostyryl)-6-azido-benzimidazole and a partially depolymerized and partially N-methoxy-methylated polycondensate of .a salt of adipic acid and hexamethylene diamine, pressing the exposed coating on a screen wetted with an aqueous alcohol, whereby the coating is transferred to the screen, washing the coating with water to remove the non-hardened portions thereof, and drying the screen and coating not removed by the Water wash.

13. A process for making screen printing stencils which comprises exposing a coated support material to light under a master, the coating comprising a first layer of photographic size' and a second layer comprising an aromatic azido compound, Nanethoxy-methylated polycondensate of a salt of adipic acid and hexamethylene diamine and a linear polycarbonamide obtained by mutual polycondensation of adipic acid hexamethylene diamine, adipic acid 4,4'-diamino-dicyclohexyl methane and e-caprolactam, pressing the exposed coating on a screen wetted With an aqueous alcohol, whereby the coating is transferred to the screen, washing the coating with Water to remove the non-hardened portions thereof, and dryilrqig the screen and coating not removed by the water was 14. A process for making screen-printing stencils which comprises exposing a coated support material to light under a master, the coating comprising a first layer of polyvinyl alcohol and a second layer comprising 4,4- diazido-stilbene-2,2'-disulfonic acid sodium salt and N-methoxy-methyl-poly-e-caprolactam, pressing the exposed coating on a screen wetted with an aqueous alcohol, whereby the coating is transferred to the screen, Washing the coating with water to remove the non-hardened portions thereof, and drying the screen and coating not removed by the water wash.

(References on following page) References Cited by the Examiner UNITED STATES PATENTS 14 3,057,722 10/1962 Alles 96-35 3,143,417 8/1964 Reichel et a1. 9635 FOREIGN PATENTS d l 9683 23 2? 96 83 5 R 16,376 11/1956 Germany. Alhers et aL A 96 83 790,131 2/1958 Great Bntam. Alexewicz et a1. 96-83 OTHER REFERENCES Smith 96-8 The Focal Encyclopedia of Photography, vol. II, 1958, Yackel 9676 The Focal Press, New York, page 1124. Neugeb'auer 96-91 10 Schmidt NORMAN G. TORCHIN, Przmary Examiner. Reichel et a1 96-83 MILTON STERMAN, Examiner. 

1. A PROCESS FOR MAKING SCREEN PRINTING STENCILS WHICH COMPRISES EXPOSING A COATED SUPPORT MATERIAL TO LIGHT UNDER A MASTER, THE COATING COMPRISING A FIRST LAYER OF A WATER-SOLUBLE COLLOID AND A SECOND LAYER COMPRISING AN ETHYL ALCOHOL-SOLUBLE SYNTHETIC LINEAR POLYCARBONAMIDE AN AN AROMATIC AZIDO COMPOUND HAVING A VINYL GROUP IN THE PARA POSITION, PRESSING THE EXPOSED COATING ON A SCREEN WETTED WITH A SOLVENT, WHEREBY THE COATING IS TRANSFERRED TO THE SCREEN, WASHING THE COATING WITH WATER TO REMOVE THE NON-HARDENED PORTIONS THEREOF, AND DRYING THE SCREEN AND COATING NOT REMOVED BY THE WATER WASH. 